Despite intensive research on ion migration (IM) in organic–inorganic hybrid metal halide perovskites, much less is known about the irradiation effect on IM in all-inorganic perovskites, especially for those single crystals lacking complicated grain boundaries. Herein, the real-time IM process and the corresponding photoluminescence (PL) spectra induced by laser irradiation in all-inorganic CsPbBr_xI_(3−x) single crystals prepared by chemical vapor deposition (CVD) were investigated. We proposed that a local electric field acts as a driving force for IM and confirmed this by applying a bias to an indium tin oxide (ITO)/perovskite/ITO configuration. According to the control experiments on CsPbBr_xI_(3−x) micro-platelets with and without polymethyl methacrylate (PMMA) coating, it is concluded that the vacancy defect on the single crystal surface is the main pathway for IM. Our work is important for understanding and controlling light induced IM in all-inorganic perovskites.